1. Field of the Invention
The present invention relates to a centrifuge rotor of the swinging bucket type and in particular to a top loading swinging bucket centrifuge rotor having a single uninterrupted knife edge pivot element supporting a sample container.
2. Description of the Prior Art
A centrifuge rotor of the type in which a sample container carrying a sample of the material to be centrifuged moves from an initial position in which the axis of the sample container is substantially parallel to the vertical center line of the rotor to a second position in which the axis of the sample container lies substantially in a plane perpendicular to the vertical center line of the rotor is known as a swinging bucket rotor.
In one typical arrangement the sample container, or bucket, used with such a rotor includes outwardly projecting elements, or trunnion pins, having a portion defining a substantially cylindrical bearing surface. The trunnion pins are typically received in corresponding support arms that are provided with conforming trunnion receiving sockets. Alternatively, the trunnion pins may be located on the arms with the corresponding sockets being disposed on the container.
In either event the bearing surface on the trunnion pin bears against the surface of the trunnion receiving socket in which it is received throughout the pivotal movement of the sample container from the initial to the second position. The trunnion receiving socket therefore acts both as the surface which supports the bearing surface on the trunnion pin and as the constraining and guiding surface which insures the controlled movement of the sample container from the initial to the second position. U.S. Pat. No. 4,400,166 (Chulay et al.), U.S. Pat. No. 3,752,390 (Chulay), U.S. Pat. No. 3,393,864 (Galasso et al.), U.S. Pat. No. 263,053 (McCollin), U.K. Pat. No. 505,446 (Baird and Tatlock), German Pat. No. 1,782,602 (Heraeus-Christ) and Swiss Pat. No. 296,421 (Willems) disclose typical examples of such rotors.
The abrading action which occurs between the bearing surface on the trunnion pin and the socket is believed to be disadvantageous for several reasons. First of all, the abrasion results in the wearing of metal which must be closely monitored. To counteract this result hardened materials are used for the pins and the sockets. Furthermore, trunnion pins require that the structure to which they are mounted exhibits relatively large radii in order to reduce trunnion stress and contact stress.
In U.S. Pat. No. 4,435,167 (Stower) an alternative support arrangement is disclosed which eliminates the above-discussed abrading action by use of a rolling profile to engender rolling action between one or more profiled surfaces. However, such an arrangement appears to prevent orientation of the container with its axis completely parallel to the vertical axis of the rotor. A rolling profile precludes the axis of the sample container from reorienting to a true vertical position after centrifugation. At zero rotational speed the sample container will hang in a true vertical position only if the line of restraint is directly in vertical alignment with the center of gravity of the sample container on the centerline of the container. The line of restraint is that location where the forces on the container are reacted. Likewise, under high speed rotation the container will assume a horizontal orientation only if the line of restraint is in the horizontal plane of the center of gravity of the container on the centerline of the container. With a rolling profile the center of gravity of the container cannot align with the line of restraint so that the container is unable to be both oriented substantially vertically while in the rest position and substantially horizontally while at speed. Since it is desirable in operation to have the axis of the sample container align with the centrifugal force field, it follows with the Stower structure that as the rotor slows and stops the axis of the container will not hang in a true vertical position.
A top loading centrifuge rotor which avoids the abrading action of the typical trunnions and the rolling action of an arrangement such as that shown in the above-discussed Stower patent is disclosed and claimed in U.S. Pat. No. 4,585,434, issued in the name of Paul M. Cole and assigned to the assignee of the present invention. This patent discloses and claims a mounting arrangement that includes a pair of knife edge pivot elements arranged to contact and support a sample container for pivotal movement along an interrupted line of contact.
In view of the foregoing, it is believed advantageous to provide a mounting arrangement for a top loading centrifuge rotor that supports the pivotal motion of the sample container from the initial to the second positions and which eliminates the shifting of the container's line of restraint and yet which does so using only a single uninterrupted line of pivotal contact.